<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>单列布局-水平居中</title>
	<style type="text/css">
		/* 第一种 margin 
		   兼容性比较好
		*/
		.box {
			border: 1px solid #f00;
			width: 90%;
			height: 200px;
			margin: 0px auto;
		}
	</style>

</head>
<body>
	<div class="box"></div>

</body>
</html>